Simple anser. Obtain a few Cleo Helena Snails, the so called Assassin snails, and introduce them to the tank. They will catch and eat any pest snail that is equal to their size or smaller. They reproduce quite slowly and are easy to control. They get to a reasonable size and are attractive. I've used them with total success to clear pest snails in my planted tanks which were swarming and eating spawns before I could get the eggs out. They partially submerge in sand or fine gravel then pop out, pursue and eat a pest snail when it goes by.